Comparison of Tower-Based and Satellite L- and C-Band Radar Backscatter from a Boreal Forest

In this study, spaceborne SAR observations were compared to the tower-based radar observations of a hemiboreal forest site in southern Sweden. BorealScat radar tower observations at L- and C-band are verified using Sentinel-1 and ALOS-2 PALSAR-2 products. For L-band, a 14-month backscatter time series was produced. For C-band, a 3.5 year backscatter time series that includes tree deaths due to a bark beetle infestation was produced. Tomographic capabilities of the tower-based BorealScat allowed both canopy-only and full forest backscatter to be analyzed. For a healthy forest, the agreement of tower-based and spaceborne SAR observations was within 0.9 dB for C-band and within 0.6 dB for L-band. Sentinel-1 backscatter was found to be insensitive to tree deaths, whereas variations were clearly visible in the tomographic tower-based backscatter. These results show that tower-based radar observations agree with those of spaceborne SARs and can be used to understand their shortcomings and identify new mission needs.